Automatic switch for use in telephone or liek systems



J 1954 c. E. BEALE'. ETAL 2,667,541

AUTOMATIC SWITCH FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed Sept. 11.1950 3 Sheets-Sheet 2 I II I u 4 r YA DW7 1 I JL 3 INVENTORS ATTORA/[YSPatented Jan. 26, 1954 AUTOMATIC SWITCH FOR USE IN'TEIlE PHONE R LIKESYSTEMS Charles Edmund Beale and Horace Edward Hopley, Liverpool,England, assignors to Automatic Telephone & Electric Company Limited,Liverpool, England, a British company Application September 11, 1950-,Serial No. 184,192

Claims priority, application Great Britain September 21, 1949 I ticaland rotary movements of the wipers and moreover employ the so-calledrectangular release facility. When a P. B. X final selector is takeninto use in the setting up of a connection, by dialling the directorynumber appropriate to the private branch exchange, the selector Wipersare initially positioned in such a manner that they are adapted to stepsuccessively over outlets corresponding to the P. B. X lines until anidle line is encountered, whereupon the call is extended over that line.

One widely used P. B. X final selector is disclosed in United StatesPatent No. 2,154,785 and this isdesigned to serve a maximum of 200 linesderived from the 10 levels of the selector bank, ach level comprising 20outlets. This selector is primarily intended for establishing connectionto private branch exchanges having a comparatively large number ofexchange lines and these would be arranged in a plurality of groupshaving more than 11 lines each or in a single group comprising up to 200lines. Now in the dialling of the directory number relevant to arequired P. B. X group, a final selector of the type mentioned is takeninto use over a group selector multiple, and the wipers are then raisedunder control of the penultimate digit dialled to a level appropriateonly to the whole or the first portion of the particular group. The lastdigit dialled is quite ineffectual and the wipers advance automaticallyinto the bank, testing a pair of lines simultaneously each time thewipers step, until an idle line is encountered whereupon the wipers arearrested and the call is extended to that line. If it occurs that thereare 20 or fewer lines in the group these are arranged in a blockstarting at the first set of contacts on the level which is exclusive tothe P. B. X group. In the event of all the lines being busy, whentested, the wipers continue to advance until the 11th position isreached and then busy tone is made audible to the calling party. On theother hand 'if the number of lines in the P. B. X group ex- 2 ceeds 20,the first 20 are arranged at outlets on the level appropriate to thepenultimate digit of the directory number, while the remaining lines areas far as possible terminated in'blocks of 20 on other levels, theremainder being connected to the earlier outlets of a final level fromwhich lines of other P. B. X groups are excluded. Thus in the case ofthe directory number relating to an over 20 line P. B. X group beingdialled, the selector wipers are raised under control of the penultimatedigit, the final digit is ineffectual as before, and the wipersautomatically advance into the bank to search for an idle line in thatpart of the P. B. X group terminated on the level. If all the outlets onthe level are busy, the wipers execute the known rectangular releasefunction, but in passing over the 11th step contacts a prearrangedcircuit condition matures whereby, after the wipers have returned to thehome position they are caused to step vertically to a level determinedby code marking relays controlled over the said 11th step contacts.Searching for an idle line then'resumes over this second level of thegroup and may subsequently continue over the remaining levels. Shouldall the lines in the P. B. X group be busy, the wipers are finallyarrested in the 11th position on the last level serving the group, andbusy tone is then made audible to the calling party.

Although a P. B. X final selector of the before-mentioned type issuitable for use in most circumstances where comparatively large groupsof P. B. X lines are to be served, it nevertheless suffers from certainlimitations, and these arise from the single digit control of thewipers. Firstly this type of control interferes with the allocation oflines within the P. B. X group to provide access to so-called nightservice extensions of the'branch exchange, which it would be ofadvantage to introduce whilst the P. B. X operator is not in attendance.In consequence night service has to be catered for by providing accessto separate night service lines by way of regular final selectors.Secondly, when a small number of lines terminate on a leve1 of the P. B.X final selector, for instance the last level of a group.

would in all probability necessitate the inconvenience of altering thedirectory numbers relating to the P. B. X groups.

A further improvement has been proposed in According to one feature ofthe invention in an automatic switch of the 'iierticaIand'i-otariZ type,the switch is provided with' twb' sets er wipers which are set on to thef rst lineof. a group of lines in response to two digits and hunt for anidle line in the group ever plurality'oif levels successively, testingtaking place 4 operating an appropriate number of times. Upon eachrelease, contacts Al apply a short circuit to relay B and also cause thelow resistance upper winding of relay Q andth'e vertical magnet VM to beenergised from earth over contacts B3, Al, DYE, D52, DXfi and DW2, relayUand contacts BN5, Cl, E5, NR! and magnet VM to battery. During theperiods of operation of relay A; relay B is "again energised in serieswith resistor YC but the magnet VM and the upper winding of relay C "arevirtually disconnected.

it renews that the vertical magnet is energised 'anurnber of timesappropriate to the penultimate digit dialled and consequently theselector wipers are raised to the required bank level. Meantime as thewipers leave the normal position the vertical oii normalcontacts aremechanically optaneously over both sets of wipers while arrangej mentsare provided to enable the switch to release rectangularly if all linesin one lei/ el are un; sesame and to' be set automatically to hunt e ranother level over which farm-er lines at thegroup areaccessible.

e eremg to another feature of the invention in an automatic switch ofthe yertical and rotary type, the switch is arranged so that the wipersare. 'set' on to the first line of a group' of lines inresponse'totwodigits' and hunt. for an idle linei'ri'the group e eeamrem of levels slice fc'es'sively'wliile if all the lines in the groupare unavailable'the wipersare'stopped on the last line of the group'an'dan individual'overflow ineter'is operated andbusy tone returned to'theeenm perty; r "r mmi g to yet another feature of the invention in an'automatic switch of the foregoing type, the settingo'f the switch on toaline other than the first withiri'a group in response to two digitscauses such line alone to be tested for its idle or busy condition;connectionbeing' made to the line if it isidle while busy ter 'eisreturned to'thecalling party if itlis eeeve ie ie; i "The invention willbe better understood from the renewing description or. on method 'e 'earI,

ing it in'tc effect. and should be r'ea'd'ih conjunctionwith'the'accompanyingdra rigs comprising Figs. rte 3; ic "shei dftpiaceei sideby side in that orderI The" dlfa l g sj fho w aLPYB. 200line final" selector, arranged 'to tes't two outlet's simultaneo ufsly,.'and' employing a' mechanism or the type di's'clos 'ed iii Britishspecification No. 39 115; nd U'nite d"states Eatent" 1 ;6 I2,124,,750.rhe, 'sele'ctorfi'sj aken eas eve meantimpri'ate set or contactsin thegreupse eeter ziiulti- PI? SM by' the application ofa loop to'the speechconductors drier. "In this event'rel'ay is operated and its contacts Alf"extendearth atv contacts 03 to relay which operates in series withrectifier MRB andresistor' YC. Consequently" contacts B l connect earthat contacts Dw and'JZ to relay oi which bperates ever its lower windingiii seris'with resisterYYF. At. the sa e time contacts B2 connectearth'at contacts nwa an'd'J'Z" to tn'e'ipe mmg 1 lead, to guar'd'tlieseieieter against ir'itru's'ion, while contacts B3 prevfi'de a holdingcircuit for: relay B'indepehd'eritly 'of' contacts C3. Relay C'inopelfating atf contacts c lprepares the impulsing path tothe'vertieel magne VM, and at'coiitacts' o3 disconnects the, originaloperating circuit.for. relay' B."

No further circuit enan'g'e take'plac' until eme digit 1 eth i fimaie di'c f h directory number; is dialled tj the selector, W FQHWH 333513: m99 Pxfi ai mfi and erated, and at contacts NI prepare the impulsing pathto the rotary magnet RM, at contacts N2 prepare to operate relay E; atcontacts N3 apply a short circuit to the lower winding of relay C, andatcontacts 'Nil prepare the release guard condition' 'The intermittentenergisation ojf the low resistance winding of relay C and the appli:cation of a sustainedshort-circuit' to the other winding ensures thatrelay C remainsoperated throughout the impulse train. Likewise relay Bremains operated due tdenergising and short:circuitingforcomplemehtary'periods. Y At the end. of the impulsetrainIrelay A re; mains'operated'tog'ether with relayfB, but the Upperwinding of relayp'is die-energised and that relay then releases afterashort delay brou ht aboutby the short-circuit at'the other winding.Upon the release of relay. C, contacts Cl dlSfiQ ik riect a'point'inth'efpath to magnet VM, while contacts C2 energise thefslow to operatrelay E over the following circuit: earthfcontacts B3, N2, BN2, DW8,DXE, DYS' and D84, relay contacts (32' and NR! and magnet VM to battery.Relay E operatesbut the vertical magnet remains inoperative due to thecomparatively high re.- sistance of said relay. RelayJE in operatingfatcontacts El prepares aselfholding circuit, at contacts E3 removes theshort-circuit "from the lower windingof relay Clso that the latter relayagain operates, and at contacts EEprepare's an impulse repeating pathfor the impulses appropriatefto. thefinal digit dialledfto therotary'm'agnetRlVi'. The opening of contacts E5. prevents the operationof relay. G upon the subsequent closureof contacts. NR2, When relay'cagain operates, contacts Cl' further "prepare the path to magnet RM; ccinta'cts'x C2 disconnect the. original operate circuit forJrel'ayv Ewhile providing analternative holding circuit oyerl contacts El,contacts, C4, disconnect point in, the path'to relay. HA, andcoritalctsfCG disconnect a point inthe path torelayDR.

when theflnex't digit, being the final digit of thedirectory number, is.dialled tothe selector, relay, 'A responds appropriately and relays B.and Cfunction in a similar mannerto that described. However, the upperwinding of relay G is now connected in seriesv with magnet RM by.contacts E5, and consequently upon each release of, relay A, earthisextended to magnet RM and the'selector wipers are'causfed to take.thev requisite number cfsteps into the. bank. Meanwhile'as the wipersstep intofthe ban}; the rotary off-normal contacts are,mechanicallyoperated, and these, at contacts NR1. prevent subsequentre.-cor"nple tion of thejoriginjal'opfilfa e circuit for. relay E atcontacts NRza'pply a short circuit to. the. lower were i C tingle, 32 Wiiria ee et epulse train, and at contacts'NR3 prepare for the operationof relay G. Upon conclusion of the impulse train, relays A and B aremaintained operated whereas relay C is caused to release after a shortdelay. Relay C again releasing, disconnect the magnet impulsing path,and at contac'ts CZ disconnects the sluggish relay E. During the-periodbetween the release of relay C and the release of relay E an outlettesting condition is extended to the appropriate PI /I bank contact viz:earth, contacts G4, rectifier MRA, contacts E4 and C4, lower winding ofrelay HA and wiper PI I. Also whilst relay E is still operated'the upperwinding of the slow-to-relea'se relay DR is connected over contacts C8,E2 and B5 to the appropriate contact on bank P2/i. I It is now opportuneto mention that the first 'lO positions on each level of the selectorbank are each separately associated with a pair-of outlets which mayextend to line circuits LC, the PI/ I and PI/2 wipers providing accessto the private wiresof the so-called odd and even-line circuitsrespectively. It should also be pointed 'out at this stage that thelocation of the P. B. X group in the bank is evidenced by thepre-arrangement of electrical potentials on the P2/ I bank contacts, thefirst pair of lines being denoted by a resistance battery condition, thelast pair by earth, and where the-P. B. X exceeds four lines, eachintermediate pair by a'disconnec'tion. Moreover the -P2/2 bank contactappropriate to the last pair of lines in each group is connected to anindividual overflow meter extending to battery.

Assume that the dialling of the two digits as described has caused theselector wipers to be set at the start of a P. B. X group. Fourpossibilities now arise, namely, that wiper Pi/ I will encounter theprivate wire of an idle line and -PI/2 the private wire of a busy line,that both Jwipers will encounter idle lines, that wiper PI /2 willencounter an idle line and wiper PI I a busy line, or that both wiperswill encounter busy 'lin'es.

' Consider that the first of the four possibilities arises. The idlecondition of the line (odd) accesisible over wipers I and +I isevidenced by a j'resistance battery at the PI I bank contact, whereasthe busy condition of the partner line '(evenY accessible" over wipers-2 and +2 is;

denoted by an earth potential at the PI/2 bank contact. It will beremembered that at this instant and for the duration of the release lagof relay E, relays HA and DR are presented to the PI I and P2 I bankcontacts respectively. These -relays therefore operate, the latter dueto the =.resistance battery condition marking the start .of. theP. B. Xgroup. Relay I-IA provides a selfiiholding circuit over its upperwinding from earth .by'way of contacts B3, N2, BN2, F4 and HA3. ContactsHAI and HA5 prepare to extend ring- -ing current to wipers I and +I, andcontacts HA2 prepare to operate relay J. Contacts HA4 ."apply guarding.earth to the private wire of the :seized line circuit, while contactsHA5 break the .outlet testing path involving relay HB. Contacts -HA!prevent the introduction of a driving ciric'uit to the rotary magnet;Although relay DR o'perates, a holding path is not provided due to theoperation of contacts HA3 so that its reten- -tion is dependent uponcontacts E2. Contacts DRI defer the release of relay E for reasons notconcerned with the present example, while cont'a'cts DB5 operate theslow-to-release'reiay DS. Contacts BS4 thereupon release relay, E andthis change.

releases relays DR and DS in turn'without them being efiective. inaddition when relay E releases, contacts El prevent its re-operation,contacts E3 'allow relay C to re-operate, and contacts E4 disconnect theoriginal path of relay HA. Contacts E5 prevent the false operation ofmagnet RM, and contacts E6 enable relay J to operate from earth atcontacts B4. Relay C now operated for the last time prepares the releaseguardcondition at contacts C3.- When relay J operates,

contacts J I connect ringing tone earth from common lead Hi tothe'm'iddle winding of relay A and consequently the tone is made audibleto the calling party in known manner. Contacts J2 prepare the meteringcircuit, while contacts J3 finally connect ringing current to the seizedline In the event of the second of the aforesaid possibilities arisingwhen the selector wipers are set at the start of a P. B. X group, namelythat wipers PI/ I and PI /2 both encounter idle marking conditions, theodd outlet constitutes the first choice. Consequently the selectorfunctions in precisely the same manner as that described with referenceto the first possibility, in that switchmg is efiected by relay HA.

Upon the occurrence of the third before-men tioned possibility, in whichwipers Pl/I and PI/2 encounter busy and idle conditions respectively,relay DR operates as already described and is then additionallyenergised over the lower winding from earth over contacts B3, N2, BN2, Fl, HA3, HB3, DB2 and C3. Contact DRI prolong the operated period ofrelay E to ensure that relay DR will remain operated over its originalpath for a suflicient period to provide for the subsequent operation ofrelay HB. Contacts DB5 operate relay D3 which at "contacts DSQ finallyallows relay E to release slowly. Contacts D'RB complete the testingcircuit for relay HB, from earth over contactss i, rectifier MR-C,contacts DRE, upper winding of relay HB, contacts HA6 and wiper PI/Z.RelayHB is therefore operated by the battery condition marking the idlePI /2 bank contact, and self-holds over contacts HB3 to earth atcontacts B3. Contacts HB3 moreover in the present case renderineffective the before-mentioned additional circuit of relay DR.Contacts HBI and H35 prepare to divert ringing current to the evenoutlet wipers. Contacts H32 prepareto operate relay J, while contactsHB4 connect-1a seizing and guarding earth to the appropriate PI/2 bankcontact. Contacts H133 connect a point in 'thepathto the test trunk bellat common lead [5 so that the insertion of a plug at points TJ I-willprovide .an audible indication that an .even outlet has circuit, afterthe subsequent release of relay E.

Contacts DB5 operate relay DS, and contacts DES. provide the usualtesting, path for relay HB.- Relay DS operating, at contacts DSIprepares for possible overflow metering, at contacts D8 2 disconnects apoint in one path tomagnet -RM, at contacts D53 disconnects the commonbusy tone lead II, at. contacts DS4 releases relay E, and at contactsDS5prepares the rotary magnet automatic stepping circuit. The eventr alrelease of relay E, at contacts E3 enables relay C to operate withoutany immediate effect, at contacts- E5 prevents the false operation ofmagnet and at contacts E5 prepares to hold relay C- in the event of allthe lines in the P. B.- X groupbeing busy. Contacts E? perform theimportant function of extending earth at contacts B4 to the rotarymagnet, whereupon the selector wipers are advanced to the secondposition of the group, and the rotary interrupters RMC are actuated- Theinter-rupters complete the opcrate circuit for relay G as follows:.earth, contacts B4; DSE, RMC, DB3 and Si, upper winding of relay G tobattery. Relay G- operating;

at contacts GI de-energises magnet. RM which restores interrupters RMQatcontacts G3 dirconnects-the hold circuit for r lay DR, which re lay itshouldbe. noted is sloW-to-release and remains operatedduring stepping.In. addition relay, G. at contacts G4 introduces the lower (lowresistance) Winding of relay. G into. the outlet testing circuits. Sinceinterrupter-s. RMC are again normal. at this stage, the original operatecircuit of relay G is broken and. the subsequent condition of relay. Gisdependent upon the busy or. idle markings now encounteredby wipersEI/LandPI-AZ.

It may. be pointed out that the four previouslymentioned'pos'sibiliti'es are again operativewith respect. to the. newlyencountered pair of. outlets. Consequently, if the odd' and. even.outlets are idle and 'busy respectively,,relay HA operates. in

series with the lower winding. of relay G. over: a inaniprovided bycontacts DB6 whilstrelay DR 50 setting 8 scribed, to extend the can werwipers ==2-, +2 and PI/2. Furthermore contacts HBI break the path tomagnet RM before. contacts GI close again.

In the event of both lines associated with the said second position ofthe P.- B. X group being busy, relays HA and HB remain inoperatiyaiandsince the lower winding of relay G is inefiectual the latter relayreleases somewhat earlier than before, so that contacts G3 prevent therelease of relay DR. Moreover contacts GI again en ergise the rotarymagnet to advance the wipers to thenext positionwhere any one of thebefore stated possibilities may obtain; The'whole process of advancingthe wiper over the bank contacts, a step at a time, and testing thecon:- ditions of each pair of outlets encountered, is repetitive until(a) an idle line is found; (19) all the outlets in the P. B. Xgroup havebeen tested or (c) the wipers reach thellth set of bank contacts on thelevel.

If the last-mentioned condition obtains. it is indicative of the dialledP. B. X group being continued on at least one other bank level.-Consequently it is required that the selector wipers shall execute theso-called: rectangular release and then be raised by a level huntingoperation to the required continuationlevel so that searching may againproceed. The operationof the selector under the said circumstances willnow be described in greater detail; Whenthe wipers attain the 11thposition on a level, the S contacts are mechanically operated. Theseat'contacts SI prevent the re-operation of relay G, and at contacts S2operate relay RN- from earth over contacts 1'33. Relay RN self-holdsover contacts R LN2 which also bring about therelease of relay DR.Contacts BN3 prepare the rotary magnet circuit", while contacts RNldisconnect a pointy in. the

- path to the release alarm earth at common lead I4. The remainingcontacts of relay RN corinect the level discriminating relays DW, .DX'D'Y and DZ to WipIS-l-Z, 2,-.I'.I and I respectively, so that thecontrolof said relaysis conditional on the presence or otherwise ofearth at the appropriate 11th ste'p contacts designate'dlW. X, Y and zcollectively. certain of the Said contacts on' each- 1eve1. may beconnectedto earthin accordance with the following table, to forrfianiarkifigcode which is to determine the next level 'It 'shoulii be notedthat contacts the rotary magnet: ishot re-energisedL If both outletsencountered? are idle when the: wipers attain; the; said secondposition. contacts DB4 and: DRE: enable relays and HR to: start: to.zoperateaovei" their lower. vzindingsi in series' with relay G.-.However, the early opening of contacts HA6 decides that only relayHAshallcomplate; the operating function, and. consequently the oddline-.circuiti isztahen' into use over wipers ----I':, H and Pt/I.

If. the? odd;.and: even outlets are busy and idle respectively, asevidenced: by

earth: and: battery markingsat: the: RI/"I and .EIXZ bank contacts relayalone: operates Laniiunctions after the manner previously? de- Considerby way of example that: the" selector Wipers: have: reached the: 11thposition on leiiel 4 and that: further lines of th'e P'. B; X- groupiareaccessible over level 3. In this event contacts X and Y on theformerlevel are connected to earth to: enable relays DX and. DY'tdoperate;- These relays,-. at contacts- DXI' and DYI prepareself holdingcircuits, at contacts DXS and DY3 prevent: subsequentv re=operation= ofrelay E,. and contacts D'X3' and DWI- in combination provide an approriate marking condition at level- 3: of the auxiliary (vertical): bankContactsDXd and. DY2 prepareto ire-operate: relay DR, and

contacts DXG prepare azpathito the rotary and vertical magnets. At this'juncture relay DR, disconnected. at" contacts BN2; releases andis:followedbyrelay DS; Thereuponarelay DS, at conta'cts5DS5 disconnects'ma-gnet' RM and-holdserelays- DX and DY,andzatcontactsDs2 further ex!tends-the pathprepared -at'contactszDXfii- Interirupters RMC arerestored upon disconnection of magnet RM, and thereupon said magnet isagain energised from earth over contacts B3, vertical magnetinterrupters VMC, contacts 'DXS and DWZ, relay C, contacts RN3, DS2,RMC, E1, GI, HB'I, HA! and NI. The wipers therefore take a 12th rotarystep, the mechanically actuated S and NR contacts restore, and thewipers return to the normal position, whereupon the vertical off-normalcontacts N restore. It may be noted that magnet RM is de-energised afterthe Wipers have taken the 12th rotary step and is then energised oncemore due to the release of interrupters RMC. However the rotary magnetarmature is mechanically restrained during the latter energisation andas a result interrupters RMC are not actuated again. Meanwhile therelease of contacts SI prepares for the re-operation of relay G. Therelease of the rotary off-normal contacts, at contacts NRI prepares apath to magnet VM, and at contacts NR3 prepares to operate relay J or G.Later, the vertical off-normal contacts restoring, at contacts NI and N2release the rotary magnet and relay RN respectively. Relay RN thenprepares to re-operate relay DR at contacts RN2, and completes aself-interrupted drive circuit to the vertical magnet as follows: earth,contacts B3, interrupters VMC, contacts DXG and DWZ, relay C, contactsRN3, Cl, E5 and NRI, and magnet VM to battery. The selector wipers,including the vertical auxiliary wiper AW, are therefore raised in stepsuntil the latter wiper encounters a suitable marking on the verticalbank, the marking in the present example being at level 3. Meantime thevertical off-normal contacts again operate, and these, in addition tovarious preparatory functions, at contacts N3 short-circuit the lowerwinding of relay C. The latter relay, which is energised intermittently,over its upper winding in series with magnet VM, during verticalstepping is sustained throughout the period due to the short-circuit atthe other winding. wiper AW attains position 3, the upper winding ofrelay C together with interrupters VMC are short-circuited from earthextending over contacts B3, D23 and DY4, wiper AW, and contacts DX3 andDWB. Consequently relay releases, after a short delay, to disconnectpermanently the vertical magnet which restores contacts VMC. Relay Calso operates relay DR from earth over contacts B3, N2, RNZ, F4, HA3,I-IB3 and C5, con.- tacts DX4 and DY2 in shunt, and contacts G3. RelayDR then self-holds over contacts DR2, prepares to operate relayG,connects points in the outlet testing paths, and operates relay DS.Relay DS is then effective at contacts D85 in releasing any leveldiscriminating relays which may be operated, relays DY and DX being released in the present example. Contacts DS5 also extend earth atcontacts Blto magnet RM which operates actuates interrupters RMC, andcauses the wipers to be set in the first position of level 3. Relays HAand HB then test the pair of outlets so encountered and switching isefiected if one of the outlets is idle. On the other hand, if bothoutlets are busy and other outlets of the same P. B. X group follow, thewhole process of searching for an idle line in that portion of the P. B.X group appearing on the continuation level proceeds in the manneralready described.

Although only the effect of one level code, i. e. that causing thewipers to be set at level 3, has been described, a perusal of thecircuit will show However, immediately that the discriminating relay orrelays, operated in accordance with remaining codes in the table,function in much the same manner as the DX and DY combination of relays.It may be mentioned that, if the lines in the P. B. X group extend overmore than two levels, searching over the appropriate levels continues,in the order determined by the condition of the discriminating relaysuntil an idle line is encountered, or until all the lines have beentested.

The operation of the circuit will now be described with reference to theP. B. X operator answering after ringing current has been applied to aseized line. Under these circumstances a di- T remove the short circuitfrom the left hand winding of relay P, which is thus enabled to operatefully in series with the holding winding of relay HA or I-IB.ContactsFl' and F5 connect the battery feed relay D to the speakingconductors. Contacts F2 and F3 disconnect ringing current path, permitrelay Dto operate over the D. C.

loop in series with barretter BRA, and moreover provide the talking pathbetween the two parties,

over capacitors QA and QB. Contacts F5 disconnect ring tone. Contacts Flintroduce the supervisory lamp LP but relay D immediately disconnectsthis circuit. Relay D moreover, at contacts D2 and D4 reverses thepolarity at the incoming speech conductors for supervisory purposes,while contacts D3 operate relay DW which is then additionally maintainedover contacts DWI to earth at contacts B4. Relay DW is ef--' fective atcontacts DWS in allowing relay J to release slowly, and at contacts DW4and DWl re spectively in removing guarding earth from the incoming Plead and connecting positive battery from common lead l2 over resistorYA to said P lead. Positive battery so connected serves to energise thecalling subscribers meter on locally originated calls and is maintainedat the incoming P lead until relay J eventually releases whereuponguarding earth is again connected. Re-

lays A, B, C, D, DW, F and HA or HB remain operated as long as theconversational connection of the selector when all the lines in a P. B.X

group are found to be busy. It will be remembered that the last bankposition of the group, which may be at any point in a level, is markedat the associated P2 /l bank contact by earth, and moreover that theoverflow meter relevant to the group is connected to the correspondingP2/ 2 bank contact. At the instant the last position is encountered theinterrupters RMC are actuated, and relay G is therefore operated bythem. Relay G holds from the aforesaid earth at the P2 bank contact andextending over con tacts B5 and E2, resistor YE, and contacts DB3 andSi. Relay G, at contacts GI prevents further energisation of the rotarymagnet, at contacts G2 prepares to connect busy tone earth, at contactsG3 allows relay DR to release slowly, and at contacts Gs temporarilymaintains the outlet testing paths, but since an idle line is notencountered relays I-IA and HB remain-inoperatil e. contacts DRZenergise the overflow meter, from earth over contacts B3, N2, BN2, F4,HA3, H333. DR? and DS!. Contacts DB3 disconnect the original holdcircuit of relay G- and substitute- Upon the eventual release of relayDR,-

another involving earth at contacts 34. Relay DR. also disconnects theoutlet testin paths and permits relay DS to release. The latter relaythen disconnects the overflow meter at contacts DSI so that theoverfiowcondition is recorded, and at contacts BS3 makes lousy tone audible tothe calling party by connecting the common tone earthlead ll.

Itmay be mentioned that when an idle line is encountered at the lastposition of the-P. B. X group-relay G temporarilyholds to earth at theP2/I bank contact but either relay HA or HE operates and is dulyfollowed by the release of relays DR, G and GS in that order, therelease of relay G being finally enacted at contacts HA2 or HBZ.Contacts HA3 or HB3 prevent overflow metering; and contacts G2disconnect the busy tone earth path before contacts BS3 restore. Inother respects the circuit functions in precisely the same manneras'when any other outlet isseized.

The selector caters for night service facilities by wayiof all or any ofthe odd lines, except the first, in the P'. B. X group. For instance ifthe P. B. 'X group extends over bank positions 45 to 55 (20 lines), ninelines may be made available for such purposes, and these would beseparately accessible by dialling the appropriate two digits in'therange 46 to 55. Thus if 46 ,is dialled to the selector, the Wipers areset accordingly in a position which is not marked by battery potentialat the PU! bank contact. Consequently relay DR does not operate upon therelease of relay 0, and it follows that a single outlet testing pathinvolving relay HA and wiper Pl/l is presented during the release lag ofcontacts E4. If the dialled night service line is idle relay HA operatesand the selector completes the connection inra manner already described.When a dialled night service line is busy relay HA remains normal, andrelay G'permanently operates, when relay E releases, from earth atcontacts B4. Relay G prevents further energisation of the rotary magnet,and causes busy tone to be made audible to the calling party.

Access to subscribers stations served by single lines is provided by theselector, but this involves the inevitable wastage of the relevant evenoutlets. Such single lines are not marked on the PM I bank, and whenthey are dialled the selector functions ina like manner to thatdescribed with reference to night service facilities.

The release of the selector after a. call will now be described, firstassuming that the release is controlled by the calling party asevidenced by the omission of the dotted connection at contacts DI. Whenthe calling party clears first relays A and B release in turn.Contacts'Bi and B2 disconnect relay C, and moreover temporarily removeearth from the incoming P lead to release the preceding equipment.Contacts B3 release relays F and HA or HB; while contacts Bi disconnectone path to relay DW. Contacts B5 disconnect wiper PZ/l, and contacts B6connect a point in the path to the release alarm earth lead l4. Relay 0releases immediately after relay B and contacts C3 introduce the releaseguard condition over operated'contacts N4. Additionally relay Creleasing, and in conjunction with relay HA or 1-13, causes theself-interrupted drive circuit for the rotary magnet to be completedfrom release alarm earthat lead M, contacts C1, B6, RN'l and DSZ,interrupters RMC, contacts/E1 and so on. The so-called rectang-ularrelease of the wipers is consequently ef-.

12 fectedland: the vertical off-normal contacts fi-i nally' release atthe home position. Meanwhile relay D is released by relay .HA or Hi3,and this brings about the-release of relay DW. The vertical off-normalcontacts releasing, at contacts N I disconnect magnet RM, and atcontacts N4 remove the guarding earth from the P lead. Thus the selectoris conditioned so as to be ready to be taken into useon anothercall. Itmaybe mentioned that should the wiper carriage fail to return 'to normaldue toamechanical' detect the permanent energisation of magnet RM'fromrelease alarm earth causes an alarm to be presented in known manner;Ifthe called party I clears first relay Dalone releases. so thatcontacts DI light the supervisory lamp LP and initiate a delayed audiblealarm condition over common lead 15.

The selector may be arranged for last party release by including thedotted connection at contacts D4 to provide an additional holding.circuit for relays F and HA or EB. The clearanceof thecalling partlyreleases relays A, B and C as before and again a brief 'unguard of theprivate, during the release lag of relay C, provides for the releaseoithe-equipment preceding the-selector. However relays D, DW, F and HA orHR remain operated until the called party clears, and thereupon theselector returns to normal. If either party fails to clear, contacts Dfor B3 cause lamp LP to light and a delayedalarm to be given.

We claim:

V 1. man automatic switchingapparatuscomprising a plurality of. levelsofbank contacts,a group oi lines terminating inadiacent contacts ondiiierent levels, two sets of wipcraanimpulseresponding device, meansfor operating :said' wipers to one of said levels in response to thereception of a. first train of impulses bysaiidimpulse-respondingdevice; means for operating said wipers to the firstof the adjacent contacts in said one level in response to-the receptionoi a second train of-impulses by said impulse-re sponding device, means.:for automatically -opcrat ng said wipers ina step-by-step action,meanseffective during saidstep-bir-stepaction for test ingsimultaneously over both- -sets of wipers the conditions of the lines.accessible through said adjacent contacts, switching means operable whenall'lines connected-to the adjacent-contacts in one level test busy,means responsive to the operation of said switching means .for returningsaid wipers to their normal'position and resetting means. forautomaticallyoperating said wiperson to the first of theadiacentcontacts inanother level.

2. Automatic switching apparatus as claimed in claim 1' including inaddition, means. responsive to the directive setting. of said wipers onan intermediate line of thegroup'for preventing the operationof saidswitching devices so that said restoring means and said resetting meansare preventedv from operating. w

3. Automatic switching apparatus comprisinglevels of .bank contacts, agroup of lines terminating in adjacent contacts. on diiferent levels,

a set of wipers, a first. source of potential oi'one' polarity connectedto a. contact accessible to-one of said wipers and corresponding tothefirst line or thergroup, a sccondsource of potential of-oppositspolarity connected to a contact accessible to said wiper and.corresponding to the last line of said group, an. impulse-respondingdevice.- 7 means for operating saidwipers to one of said:

levels in response to the reception of a first train of impulses by saidimpulse-responding device, means for operating said wipers to the firstof the adjacent contacts in said one level in response to the receptionof a second train of impulses by said impulse-responding device, a firstswitching device operated over said wiper from said first source ofpotential, means responsive to the operation of said switching devicefor automatically operating said wipers in a step-bystep action to testthe condition of the lines connected to said adjacent contacts in saidone level, first and second switching means operable in the event thatall said lines accessible to said adjacent contacts test busy during thestep-by-step operation of said wipers, means for restoring said wipersto their normal position in response to the operation of said firstswitching means, means for resetting said wipers on to the first one ofadjacent contacts on a different one of said levels in response to theoperation of said second switching means, a second switching deviceoperated over said wiper from said second source of potential and meansresponsive to the operation of said second switching device forterminating said hunting operation and for transmitting busy tone.

4. Automatic switching opparatus as claimed in claim 3 including, inaddition, an overflow meter connected to a contact accessible to asecond wiper and corresponding to the last line of the group and meansresponsive to all lines in the group test busy during said step-by-st'epaction for completing a circuit for said overflow meter over said secondwiper.

CHARLES EDMUND BEALE.

HORACE EDWARD HOPLEY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,556,987 Christian Oct. 13, 1925 1,603,929 Wicke Oct. 19,1926 1,631,506 Sipe June 7, 1927 1,638,513 Stehlik Aug. 9, 19271,667,950 Ruggles May 1, 1928 1,674,677 Bascom June 26, 1928 1,694,623Ostline Dec. 11, 1928 1,716,986 Stehlik June 11, 1929 1,812,999 Tayloret a1. July 7, 1931 2,419,282 Ostline Apr. 22, 1947

